What is approach velocity and device velocity.I have faced this problem during defing blcoakeg.Also I have a few problems when defining blockages. First is in my case I have to define a blcoakge in a domain.In that blcokage there is 40 percent area is open.Actually there is some tubes at taht place ,but instead modelling them i have taken blckage because i know the pressure drop taking from those tubes.Now for that i have to define that 40 percent area is open.Soi how i can define it in cfx?second thing is how to define head loss co effcient for that? i have gone through manual in tha tther are loss co eff like resistance loss co eff,diractional loss co eff etc etc.so is ther any relation of head loss with these co eff? and what is permeabilty here?Pls answer this ifanybody know. Thanks all of u in advance.

I think that the loss coefficient is set in opening bounduary condition, more specifically in: loss coeficient!!

For isotropic loss model, dP/L~Cr1*U+Cr2*U^2. L is the thickness of porous domain. Cr1 is linear resistance coef, Cr1=viscoity/permeability coef. Cr2 is quadratic resistance coef, Cr2=resistance loss coef*density/2. If you know pressure drop, you can estimate Cr1 and Cr2 using above relationship.

Thaks sir,but in my case there is 40 percent opening in blockage.so how to define that 40 opening i.e. porosity ?

If you define a porous domain in CFX-10, you have options to specify porosity or loss model. For porosity, you give volume porosity, while loss model has two choices: isotropic or directional loss model.